The old master at Speedliner Boats taught me how to scarf using a hand
plane, a belt sander and a sharp eye. I made a scarifying joint jig to hold
a router but was much happier with the hand method I was taught. Wooden
Boat magazine usually has an ad for an attachment for a Makita electric
planer. Though I have never tried it.

It's not really that hard when you get the hang of it.

Don Dando